1. Field of the Invention
The present invention relates to ways to block ultra violet (UV) radiation from high intensity light sources such as arc tubes, and in particular, an apparatus and method of blocking UV radiation at or near the light source.
2. Problems in the Art
The use of and applications for high intensity light sources continues to increase. One example is wide area lighting, such as for lighting sports fields or arenas.
A popular type of high intensity light source in use today is referred to as a metal halide source. A arc tube comprising literally a tube made of, for example, quartz, includes two electrodes entering opposite ends of the arc tube. As is well-known in the art, certain chemicals are inserted into the arc tube and it is sealed.
By providing electrical power to the electrodes, the chemical make-up of the interior of the arc tube results in the emission of light.
While such a light source can provide a very high intensity of light for its size and for the power consumed to generate such light, one problem or concern is that such light includes an ultraviolet component. Ultraviolet light can be harmful to humans. Because such arc tubes can be used to produce an intense source of light, this is a very real concern.
Rules and regulations have been developed by the industry addressing this problem. Examples of presently used solutions are as follows.
A glass jacket can be placed around the arc tube. For reasons known in the art, regular glass (as opposed to the high temperature quartz glass used for the arc tube) has properties which block UV radiation, or at least a substantial part of it, whereas quartz such as used with the arc tube does not. Thus, this what will be called xe2x80x9cregular glassxe2x80x9d effectively acts as a filter for UV radiation. When associated with a jacket around the arc tube, at a sufficient distance that the heat from the arc tube will not materially affect the jacket, such glass blocks UV radiation from the light source. Although such solutions are relatively inexpensive, it increases the structural complexity of the light source and the manufacturing process. There are more things subject to failure.
Also, a subtle but important point is that a glass jacket increases the overall size of the light source. As is appreciated in the art, it is generally true that the bigger the physical size of the light, the bigger the physical size of the fixture must be. The converse is also many times true. As can be further appreciated, it is generally advantageous to minimize the size of lighting fixtures. Smaller size usually means less materials and less manufacturing costs. Particularly in outdoor applications, such as outdoor wide area lighting of sport fields, a smaller physical fixture size reduces the wind drag or wind load on the fixture.
Furthermore, it should be understood that jacketed arc tubes create glare problems not created by non-jacketed arc tubes. Any time light passes through glass, there is some reflection. Therefore, some of the light generated by an arc tube would reflect off the jacket wall. This causes the jacket to glow, which in turn presents a larger source of glare when the interior of the fixture is viewed.
Another solution to the problem of UV light from an arc tube uses regular glass in the lens of the light fixture as a UV filter. The advantage of this system is that it eliminates the need for the jacket around the arc tube. The size of the light source can then be smaller which can be very useful in lighting applications.
Each of the above solutions has further deficiencies or problems, however. Utilization of the jacket to filter UV light is beneficial because if the lens to the fixture is opened with the light on, UV radiation would continue to be blocked. If the lens only is used as the UV filter, one who opens the lens (a conventional way to access the interior of many fixtures), would then be exposed to UV radiation.
However, if the lens to the fixture is broken, UV radiation would emanate from the fixture if the light source is on. Moreover, in situations where a UV filter is associated with a jacket around the arc tube, if the jacket breaks or is removed, UV radiation may be a problem.
Therefore, certain additional precautions have been made with many lighting fixtures in the industry. In particular, many fixtures which utilize an arc tube without a jacket, but rely on the lens to block UV, have safety switches or components that cut power to the arc tube if either the lens is opened or the lens breaks. This adds complexity and cost to the fixture. Also, the safety provided by such power disconnect components is only as good as the reliability of the system and the components. Over time they may degrade and malfunction.
Heretofore, no one is known to have placed a UV filter directly on the arc tube. Because of the high temperatures of such high intensity arc tubes, it is difficult to make any substance adhere, at least for substantial periods of time.
There is therefore a need for an improvement in the arc regarding this issue.
It is therefore principal object of the present invention to provide an apparatus and method for blocking ultraviolet radiation from high intensity arc tubes which solves the problems or improves over the deficiencies in the arc. Further objects, features, and advantages of the invention include:
1. An apparatus and method which block ultraviolet radiation from arc tubes at all times.
2. An apparatus and method which eliminate the need for jackets around arc tubes.
3. An apparatus and method which eliminate one need for safety switches or power cut-offs.
4. An apparatus and method which make it possible to utilize high intensity arc tube light sources of the smallest possible physical dimensions in the fixture and can allow reduction is size of the entire fixture.
5. An apparatus and method which is durable and economical.
These and other objects, features, and advantages of the present invention will be become more apparent with reference to the accompanying specification and claims.
The present invention is an apparatus and method for blocking UV radiation from high intensity arc tubes. The method of the invention includes placing an ultraviolet filter coating directly on the arc tube. The coating effectively blocks or filters at least a substantial amount of the UV radiation generated by such an arc tube and yet passes a substantial amount of useable light from the light source.
The apparatus of the invention includes an arc tube having a body of a certain size. The coating can be placed on part of or all of the arc tube envelope. The light source therefore has a physical size which is essentially the same as the arc tube.